The present invention relates to a power transmission system and a method for diagnosing a power transmission system.
Inductive power transmission systems are known. Inductive power systems of this kind are used for charging the traction battery of an electrical hybrid vehicle, for example. During transmission of the power by an inductive charging system of this kind, strong magnetic alternating fields are produced in the air gap between primary coil and secondary coil. In this case, the magnetic field strength of such alternating fields increases in proportion to the reduction in the coil size of the coils used. The magnetic alternating fields that arise in this case can, from a certain strength upward have negative effects on the nervous system of living creatures, such as human beings or animals. Therefore inductive power transmission systems of this kind are equipped with an apparatus for detecting or identifying objects. When an object is detected in the air gap between primary coil and secondary coil in an inductive power transmission system, the capacity of the power transmission is then reduced or if need be the power transmission is stopped completely. The power transmission process can then be continued only when it is certain that there is no longer an object in the air gap of the inductive charging system.
One option for the identification of foreign objects in the air gap of the inductive power transmission system consists in conventional inductive metal detection by means of additional test coils that are excited in pulsed fashion. Other methods are based on 2- or 3-dimensional object identification methods.
The German patent application DE 10 2009 033 236 A1 discloses an apparatus for the inductive transmission of electric power from a stationary unit to a vehicle. The apparatus has a device for detecting the presence of an article within a predetermined space. The detection device has at least one contactless sensor and an evaluation device connected to the sensor. The sensor may be an ultrasonic, radar or infrared sensor or an electronic image sensor.
Foreign object identification is a safety-relevant function of the charging system. Therefore, the operational state needs to be made reliable if need be by means of redundant sensor systems and/or monitoring of the sensitivity of the sensor system. A malfunction in the foreign object identification needs to be reliably identified.
There is therefore a need for a power transmission apparatus for inductive power transmission that allows the foreign object identification to be monitored. In addition, there is also a need for a diagnosis method for a power transmission system with foreign object identification.